When cosmic rays and Earth collide

This article, written by Barbara Kennedy and featuring the work of Penn State scientist Stephane Coutu, originally appeared in the Centre Daily Times (CDT) on 28 October 2012 in the bimonthly "Focus on Research" column, which highlights different research projects being conducted at Penn State.

Artistic impression of cosmic rays entering Earth's atmosphere. Credit: CERN/Asimmetrie/Infn.

Cosmic rays are miniature bullets from space with so much energy that they can actually destroy atomic nuclei in a mini nuclear explosion when they slam into Earth’s atmosphere.

The “rays” are naked nuclei, atoms stripped of their electrons. Some can rip apart even the dense nucleus of an atmospheric atom, breaking the powerful bonds between its fundamental particles. The shrapnel from the pulverized atoms rains down as a shower of ionizing radiation, much of which accumulates at the altitude where jet airplanes fly, exposing flight crews to as much work-related radiation as uranium miners.

This is just the basis of what Stephane Coutu, a physicist at Penn State, studies. Along with colleagues and students, Coutu is working to solve mysteries that began when cosmic rays were discovered 100 years ago. What gives the most powerful cosmic rays so much energy and shoots them in our direction? How do cosmic rays affect our planet’s fragile atmosphere and life here on Earth?

“Radiation can cause genetic mutations,” Coutu said. “If these mutations improve an animal’s chances of survival, they get passed on to future generations, changing the course of that species’ evolution.”

Extraordinary experiments are underway to discover new knowledge about cosmic rays and the radiation they create. One of the discovery teams, led by Coutu, has made annual expeditions to Antarctica since 2004 to launch giant balloons that lift cosmic-ray detectors 120,000 feet to the edge of Earth’s atmosphere to measure the incoming cosmic rays before evidence of their nature is lost in collisions with Earth’s atoms.

Why go all the way to Antarctica to launch balloon experiments? Coutu said that “it costs about a thousand times less to send up an instrument on a balloon than on a rocket or a satellite, so we prefer balloon launches whenever they can be effective for our research.”

Another cost-saving advantage is that research balloons launched from Antarctica can fly without fuel for weeks, trapped in the stable vortex of wind circling high above the South Pole.

The CREST balloon payload, hanging from the launch crane at the right in the distance, just prior to launch by high-altitude balloon from the Ross Ice Shelf near McMurdo station, Antarctica, on Christmas Day 2011. Credit: Stephane Coutu, Penn State University.

At the end of the flight, perhaps as long as 40 days, the balloons are remotely separated from a large parachute, which allows the payload to land conveniently near the launch site at McMurdo Station.

Penn State researchers have participated in many such experiments. The most recent, the Cosmic Ray Electron Synchrotron Telescope, flew for the first time in December and landed in January after collecting clues that Coutu is now analyzing.

So far, scientists have learned that most, but not all, of the cosmic rays crashing into our atmosphere likely come from stars exploding inside our Milky Way galaxy. Expanding shells of stardust in the supernova remnants blast from the powerful explosions, creating shock waves that launch the cosmic-ray particles into space — like surfers riding gigantic waves.

Coutu said the rarest and most energetic of these shockwave-propelled particles — those that travel at nearly the speed of light — are the most intriguing because their origin is the most challenging to explain.

“They appear to be coming from supermassive black holes in the centers of distant galaxies — one of the most powerful energy sources in the universe since the Big Bang. These black holes produce enormous amounts of energy in narrow jets as they devour dust, gas, and even entire planetary systems,” he said.

Because balloon experiments can’t detect enough of these rarest cosmic rays, scientists have invented a menagerie of new technologies for studying them. Some of these new detectors are buried deep in the Antarctic ice, some are spread throughout a huge landscape in Argentina, some are in mines miles underground, and one that Coutu is helping to build is destined for the International Space Station.

Another mystery that intrigues Coutu is whether surprising uses will emerge for the new cosmic-ray-research technologies.

“The Internet was invented by particle physicists who wanted to exchange scientific data in a way that was fast, transparent, and easy. The protocols they invented resulted in the World Wide Web,” he said. “Nobody knew then what impact this new research technology would have now on so much of everything else.”